A certain disease affects about 1 out of 10, 000 people. There is a test to check whether the person has the disease. The test is quite accurate. In particular, we know that • the probability that the test result is positive (suggesting the person has the disease), given that the person does not have the disease, is only 2 percent; • the probability that the test result is negative (suggesting the person does not have the disease), given that the person has the disease, is only 1 percent. A random person gets tested for the disease and the result comes back positive. What is the probability that the person has the disease?

You draw one card at random from a standard deck of 52 playing cards. What is the probability that the card is either an ace or a spade?

You attend a karaoke night and hope to hear your favorite song. The karaoke song book has 300 different songs (your favorite song is among them). Assuming that the singers are equally likely to pick any song and no song repeats, what is the probability that your favorite song is one of the 20 that you hear that night?